Standard cling signage comprises releasable flexible plastic films having visual indicia printed on one side thereof. The plastic film is typically a highly plasticized polyvinyl chloride approximately 0.016" thick. This film requires the use of a heavy gauge release paper to support it during the printing process. When the film is placed against a flat surface, usually glass, it clings to the surface. The film is easily released from the surface and can be re-adhered to a surface several times. The present drawbacks with cling signage are that it is difficult to print on the highly plasticized PVC film, the cost is relatively high, it is relatively bulky, and it is difficult to apply at cold temperatures. Perhaps the most significant drawbacks are the cost and difficulty of printing on the highly plasticized surface. Furthermore, the films cannot be used in existing printing machines and/or copy machines.
The present invention embodies a laminated sheet for cling signage. The sheet overcomes all of the limitations of cling PVC signage and particularly, the sheet of the invention is processable on all copy machines, computer printers, pen plotters, offset and litho presses and screen printers. The sheet of the invention is relatively thin, 0.00048" to 0.00100", compared to prior art cling signage, 0.016". This thinness allows the sheet to be used in all types of computer printers and copy machines.
The sheet as a minimum comprises a support film, i.e. a polyester film, a print receptive coating on one side of the film and an adhesive coating on the other side of the film. The print receptive coating is selected based on its ability to adhere to the film and its receptiveness to have an image formed thereon. That is, depending upon whether the sheet of the invention is to be used with a laser printer, color ink jet printer, lithopress, etc., the print coating will be selected based on the intended printing process.
The adhesive coating is referred to herein as a cling elastomeric coating. As will be described, it distinguishes from those coatings commonly referred to as pressure sensitive adhesive coatings in that it does not loose its effective adhesive characteristics over a series of repeated applications as do most pressure sensitive adhesive coatings.
Broadly, the sheet comprises a plurality of layers including a top layer which is a print receptive coating. The print receptive top layer can be customized to work with all types of commercially available ink and imaging systems.
The print receptive coating will vary in composition depending on the print market in which it will be used. Styrene/acrylic polymers with silica fillers are known to work in thermal transfer printing. Polyester or acrylic polymers with silica fillers are known to work in copy machines, laser printers, dot matrix, offset, litho and screen printing applications. Polyvinyl pyrrolindones and ethyl celluloses are known to work in ink jet applications. Print receptive coatings have been developed for polyethylene terphalate and other orientated films that work in all the different types of printing equipment. Although attempts have been made, as a practical matter, nothing can be done to make the polyvinyl chloride cling signage processable on copy machines and computer printers.
The next adjacent layer is an oriented film to provide structural integrity to the sheet when used as signage. This layer is an oriented film that will vary in thickness and type dependent on the application and market. Both clear and opaque white polyethylene terphalate and biaxially oriented polypropylene in thicknesses ranging from 0.00048" to 0.00100" can be used depending on the end use market.
The next adjacent layer is a coating of a cling elastomer. The cling elastomer used in the preferred embodiment of the invention has a Tg of -65.degree. C. which allows a functional temperature range of -65.degree. C. to 160.degree. C. compared to the 0.degree. C. to 80.degree. C. range of the prior art polyvinylchloride. The cling elastomer used is not a pressure sensitive adhesive and can be cleaned and reused indefinitely. Pressure sensitive adhesives, once contaminated, no longer adhere.
The cling elastomeric coating will vary in thickness and polymer type dependent on application and end market. The elastomers of choice are either silicone or polyurethane based. Platinum catalyzed addition cured silicone polymers are preferred because of their processing advantages. Diphenylmethane diisocyanate or toluene diisocyanate cured urethanes are also preferred because of their low modulus and processing advantages.
The next layer is a film to protect the elastomer and to provide dimensional stability to the sheet. The layer preferably is an oriented film or polycoated paper that will vary in thickness and type dependent on the market. This layer's function will be to protect the elastomer from contamination and to provide physical support to the construction during the printing process.
The next and last layer is a friction coating such as polyester filled with silica to facilitate the use of the sheet in conventional printing and copying machines.
The print receptive layer, elastomers and friction layer are applied in roll to roll processes that include but are not limited to the following types of coating methods: meyer rod, gravure, offset gravure, reverse roll, knife over roll and slot die. The proper combinations of the layer thicknesses can be used to allow processability on all copy machines and computer printers.